Combination bearing materials

ABSTRACT

This invention relates to the manufacture of rolling-contact bearings wherein the outer and inner races or rings were hitherto made of the same steel grade and subjected to a heat treatment with or without a preliminary cementation. According to this invention, the inner races of the bearings are made of cementation steel and the outer races as well as the rolling-contact members, such as balls and rollers from corehardened alloy steel. The treatment consists of a case-hardening or cementation applied to the inner races and of a hardening process applied to the outer races and rolling bodies.

United States Patent 1 Beauchet 1 May22,1973

[54] COMBINATION BEARING MATERIALS [75] Inventor: Jean Beauchet, Annecy (Haute Savoie France [73] Assignee: Societe Nouvelle De Roulements, An-

necy (Haute Savoie), France [22] Filed: Oct. 29, 1971 [21] Appl. No.: 194,069

Related US. Application Data [63] Continuation of Ser. No. 4,729, Jan. 21, 1970, abandoned.

[52] U.S. Cl ..308/l73 [51] Int. Cl. ..F16c

[58] Field of Search ..308/8, 2, 241, 237, 7 308/177 [56] References Cited UNITED STATES PATENTS 3,275,389 9/1966 Neilson et a1 .308/8.2

Primary Examiner-Charles J. Myhre Assistant Examiner-Frank Susko Attorney-Stevens, Davis, Miller & Mosher [57] ABSTRACT This invention relates to the manufacture of rollingcontact bearings wherein the outer and inner races or rings were hitherto made of the same steel grade and subjected to a heat treatment with or without a preliminary cementation.

According to this invention, the inner races of the bearings are made of cementation steel and the outer races as well as the rolling-contact members, such as balls and rollers from core-hardened alloy steel. The treatment consists of a case-hardening or cementation applied to the inner races and of a hardening process applied to the outer races and rolling bodies.

2 Claims, 2 Drawing Figures 1 COMBINATION BEARING MATERIALS This is a continuation of application Ser. No. 4,729, filed Jan. 21, 1970, now abandoned.

The present invention relates to a novel method of utilizing materials hytherto used in a conventional fashion in the manufacture of races or rings of rollingcontact bearings, such as ball-bearings and taper-roller, barrel-rollers or cylindrical-roller bearings, and the like.

It is already known in the manufacture of bearing races to use chromium steel alloys of a grade corresponding substantially as a rule to the alloy 100 C 6 according to the French Standards AF NOR NF A 35 551, or to the American Standards SAE J 404 F, i.e., alloys of which the composition lies approximately within the following percent limits (by weight) C 0.95 to 1.10, Cr 1.50 to 1.60, Ni 0.30, Mn 0.25 to 0.40, Si 0.10 to 0.35, P S 0.025, the residue being Fe.

It is also known to manufacture bearing races or rings from cementation or case-hardened steel, i.e., of which the composition lies within the following limits given in percent by weight C 0.15 to 0.25, Si=0.20 to 0.35, Mn 0.30 to 0.60, Cr= 0.20 to 0.60, Ni 1.65 to 2.00, Mo 0.20 to 0.30, A1 0.015 to 0.045, P S 0.055.

In either case the steel hardness necessary for a satisfactoryoperation and useful life of the bearing is obtained by submitting the parts to a suitable heat treatment.

In the case of a steel of the above-defined grade 100 C 6" having a relatively high carbon content this treatment consists of a hardening step causing the parts to acquire a relatively high and substantially constant hardness throughout the mass of the treated material.

In the case of cementation or case-hardened steel the initial material is a low-carbon and therefore nonhardening" steel. Then this material is surface-enriched with carbon by applying a suitable cementation process to a variable depth which however is always very reduced in comparison with the total mass or thickness of the part. Then, the part is hardened in order to obtain in the carbon-enriched film a hardness comparable with that of the aforesaid steel grade 100 C 6. The

hardness of the remaining portion of the part which has retained its initial composition is not increased appreciably but nevertheless this portion reserves a very good core resilience.

However, the heat treatment of a steel is attended by tresses developing at the outer periphery of the treated parts. In the case of core-hardening steel, the hardening process begins at this outer periphery. The resulting change of structure is attended by an increment in the specific volume of the part and when the core thereof is hardened in turn this causes traction stresses to develop in the outer peripheral film or layer of the art. On the other hand, in the case of cementation steel, the internal structure of the part remains substantially unchanged and counteracts any tendency of the peripheral film or outer layer to increase in volume, so that the surface layer of the part become compressionstressed.

On the other hand, cementation steel parts have a better core resiliency than core-hardening steel parts and therefore are less fragiles in case of shocks.

Finally, the heat treatment of a steel with a view to increase its hardness is attended not only by an increased fragility but also by a distortion of the treated parts, as a consequence of the above-described stress effects, this distortion being frequently too important to be removed during the subsequent grinding and super-finishing operations. The distortion is considerably more pronounced in the case of cementation steel parts than in the case of alloy steel parts of the C 6 grade, for these parts are subjected to two successive operations, notably the case-hardening operation taking place at a temperature higher than that at which the parts made of said 100 C 6" alloy steel are maintened before hardening them.

It is the essential object of the present invention to minimize these inconveniences by combining the use of these materials in the manufacture of rolling-contact bearing parts with a view to takethe best advantage of their properties as a function of the service, mounting and manufacturing conditions and requirements of these parts.

Rolling-contact bearings according to the present invention are shown in the accompanying drawings wherein:

FIG. 1 is a partially schematic, plan view of a bearing shown in the direction of its axis of rotation.

FIG. 2 is a partially schematic, cross-sectional view of the bearing shown in FIG. 1, taken along line 11-11 of FIG. 1.

The method of manufacturing rolling-contact bearings according to this invention is characterized by the use, in combination, of materials hardened and prestressed by heat treatment so that the inner and surface stresses developed during this treatment and known per se counteract and compensate the stresses subsequently developing during the mounting and service of these parts, in order to reduce the strain thereof.

The method of this invention consists more particularly in making the inner races 10 of rolling-contact bearings (as shown in FIGS. 1 and 2) from cementation steel and the outer races 11 as well as the rolling members 2 of these bearing from core-hardening steel alloy. In either case the steel and the heat treatment to be applied thereto are elected with a view to produce parts having a suitable hardness of the order of 62 HRc points.

With this manufacturing method the distortion of the parts is reduced to a minimum since the part most subject to distortion, i.e., the outer race having a reduced cross-section in proportion to its dimensions, and more particularly the races of taper-roller bearings, are made of core-hardening steel. The manufacture of the inner race of cementation steel is troublefree as far as distortion is concerned for this part is considerably thicker and does not show any appreciable distortion after the heat treatment.

On the other hand, the manufacturing technique according to this invention is attended by advantageous features for certain applications from the point of view of the strength of materials. The inner races of rollercontact bearings are fitted as a rule on the corresponding shafts with a certain degree of tightness, whereby these races are more or less stressed and this, added to the stresses resulting from the service loads supported by the shafts, increase the fragility of the parts in case of shocks. This condition is particularly true in the case of taper-roller bearings due to the presence of flanges which may undergo important flexion stresses.

In this case. the fact of making these parts from cementation steel permits of reducing this fragility in case of shocks because these parts combine a good core resilience with compression prestress in the outer layer which will counteract he traction stress resulting from the load and also from the fitting of'the parts on their shafts.

On the other hand, as the dimensions of the inner race or ring are considerably smaller than those of the outer race or ring (notably in the perimeter of the race working surface pro-per), the stress exerted thereon per surface unit is higher and as a rule its useful life is shorted.

Due to the greater elasticity inherent to the underlying layer of a cementation steel part in comparison with a core-hardened steel part, the inner race or ring will have a higher fatigue strength if it is made from cementation steel.

Regarding the outer race it is generally fitted with a certain tightness in the bore intended therefor. Thus, the resulting compression prestressing of the bearing race is advantageous since it counteracts directly the stress resulting from the load supported by the shaft and transmitted to the working surface of the outer race via the inner ring and the rolling members (balls or rollers). This prestressed condition of the race forming metal layer of the outer ring is improved if the metal utilized in its manufacture displays after the heat treatment a homogeneous structure and a homogeneous hardness promoting the stress transmission through the material of the part concerned.

Therefore the manufacture of outer races or rings from core-hardening steel is advantageous from the strength of material point of view and permits of minimizing distortion likely to result from the heat treatment.

Regarding now the rolling-contact members (balls, rollers, etc.), these may advantageously consist of corehardened steel or the following reason when two bodies are in mutual rolling contact it is known that the coefficient of friction of the bearing is improved if these bodies are of different natures. If both bodies are made ing contact member and the outer ring race, for as already explained hereinabove, the inner ring is more frequently stressed than the outer ring, and with a greater intensity since the two bodies involved have curvatures of opposite sign.

For these various reasons it is advantageous to make the rolling bodies and the inner races or rings of bearings from metals of different relationships, i.e., to use core-hardening steel for the rolling bodies and cementation steel for the inner races or rings.

I claim:

1. A roller-contact bearing comprising:

an outer race,

a plurality of rolling members within said outer race,

said outer race and said rolling bodies comprising a relatively high-carbon steel which is surfacehardened 'and tension pre-stressed at their running surfaces, and

an inner race comprising a relatively low-carbon cementation steel which is case-hardened and compression pre-stressed at its running surface.

2. The roller-contact bearing of claim 1, wherein saidrelatively high-carbon steel is a composition comprising by weight:

about 0.95 to about 1.10 per cent carbon;

about 1.50 to about 1.60 per cent chromium;

about 0.25 to about 0.40 per cent manganese;

about 0.10 to about 0.35 per cent silicon;

not greater than about 0.30 per cent nickel;

not greater than about 0.025 per cent total phosphorus and sulfur;

the remainder of said relatively high-carbon steel composition being iron; and wherein said relatively low-carbon steel is a composition comprising by Weight:

about 0.15 to about 0.25 per cent carbon;

about 0.20 to about 0.35 per cent silicon;

about 0.30 to about 0.60 per cent manganese;

about 0.20 to about 0.60 per cent chromium;

about 1.65 to about 2.00 per cent nickel;

about 0.20 to about 0.30 per cent molybdenum;

about 0.015 to about 0.045 per cent aluminum;

not greater than about 0.055 per cent total phosphorous and sulfur;

the remainder of said relatively low-carbon steel composition being iron. 

1. A roller-contact bearing comprising: an outer race, a plurality of rolling members within said outer race, said outer race and said rolling bodies comprising a relatively high-carbon steel which is surface-hardened and tension prestressed at their running surfaces, and an inner race comprising a relatively low-carbon cementation steel which is case-hardened and compression pre-stressed at its running surface.
 2. The roller-contact bearing of claim 1, wherein said relatively high-carbon steel is a composition comprising by weight: about 0.95 to about 1.10 per cent carbon; about 1.50 to about 1.60 per cent chromium; about 0.25 to about 0.40 per cent manganese; about 0.10 to about 0.35 per cent silicon; not greater than about 0.30 per cent nickel; not greater than about 0.025 per cent total phosphorus and sulfur; the remainder of said relatively high-carboN steel composition being iron; and wherein said relatively low-carbon steel is a composition comprising by weight: about 0.15 to about 0.25 per cent carbon; about 0.20 to about 0.35 per cent silicon; about 0.30 to about 0.60 per cent manganese; about 0.20 to about 0.60 per cent chromium; about 1.65 to about 2.00 per cent nickel; about 0.20 to about 0.30 per cent molybdenum; about 0.015 to about 0.045 per cent aluminum; not greater than about 0.055 per cent total phosphorous and sulfur; the remainder of said relatively low-carbon steel composition being iron. 